Particle-rod nano structures and method of forming same by spin coating

ABSTRACT

A method of forming a particle-rod nanostructure is disclosed. The method comprises preparing a mixture comprising an inorganic nanoparticle and an organic molecule in a solvent. The method further comprises spin-coating the mixture to nucleate a crystal growth of the organic molecule on the inorganic nanoparticle deposited on a substrate, yielding the particle-rod nanostructure.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/700,611, filed on Jul. 19, 2005, entitled “PARTICLE-ROD NANOSTRUCTURES AND METHOD OF FORMING SAME,” the entire contents of which areincorporated herein by reference.

FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with government support under Contract Nos.CTS-0221586 and CTS-0216109 awarded by the U.S. National ScienceFoundation. The U.S. government may retain certain rights to theinvention.

FIELD OF THE INVENTION

The present invention relates to particle-rod nanostructures. Moreparticularly, the invention relates to a method of forming aparticle-rod nanostructure by spin-coating a mixture comprising cappednanoparticles and fatty acids in solvent.

BACKGROUND OF THE INVENTION

Organic-inorganic hybrids form the basis of biomineralization.Organic-inorganic hybrids may be used for electronic, optical, andbiosensing applications. Such materials combine and enhance thefunctionalities of different material groups. For example, junctionsbetween self-assembled monolayers and metal nanoparticles allow for thestudy of single electron transfer processes. Room temperaturelight-emitting diodes (LEDs) are created by the incorporation of a dyemolecule within a perovskite framework. Attachment of oligonucleotidesto gold nanoparticles triggers the self-assembly of DNA/nanoparticlearrays for biosensing and DNA sequencing.

With the drive towards device miniaturization, there is a desire forfunctional units such as nanoparticles and nanorods to be connected in apredefined manner. Thus, in addition to the synthesis of nanoparticlesand nanorods, an emerging focus is on connecting and assembling thevarious nano-units.

BRIEF SUMMARY OF THE INVENTION

The present invention generally provides a method of formingparticle-rod nanostructures. Organic molecules, such as alkanederivatives, form a two-dimensional crystalline stripe phase layer onhighly oriented pyrolytic graphite. It has been found thatmolecule-capped inorganic nanoparticles, e.g., nanoparticles of cadmiumselenide capped by mercaptoundecanoic acid (MUA-CdSe nanoparticles),nucleate single-crystalline rods of organic molecules with across-section of a single unit cell.

One example of the present invention provides a method to nucleateorganic crystalline rods from inorganic nanoparticles by spin coating.The solution-based method potentially allows for precise tuning of thewetting profile of the solution on surface-attached nanoparticles,providing the reservoir for the growth of single crystalline rodsthereon. The results show that that nanoparticles may be used asheterogeneous seeds for the nucleation of guest crystals.

In another example, the present invention provides a spin-coating methodto nucleate organic crystalline rods of uniform size from an inorganicnanoparticle on a solid surface. The particle-rod hybrid structurespontaneously forms when a film is spin coated from a mixed isopropanolsolution of arachidic acid and nanoparticles of cadmium selenide cappedby mercaptoundecanoic acid (MUA-CdSe nanoparticles) on graphite. Atomicforce microscopy (AFM) images show that MUA-CdSe nanoparticles nucleatesingle-crystalline rods of arachidic acid with a cross-section of asingle unit cell of the C-form.

In yet another example, the present invention provides a method offorming a particle-rod nanostructure. The method comprises preparing amixture comprising inorganic nanoparticles and organic molecules in asolvent. The method further comprises spin-coating the mixture tonucleate a crystal growth of the organic molecule on the inorganicnanoparticle deposited on a substrate, yielding the particle-rodnanostructure.

In yet another example, the present invention provides a particle-rodnanostructure comprising an inorganic nanoparticle coated with a cappingagent. The nanostructure further comprises an organic molecule nucleatedon the capped inorganic nanoparticle in a one-dimensional growthpattern.

In another example, the present invention provides a particle-rodnanostructure system. The system comprises a film laminate including anorganic stripe phase layer deposited on a substrate, a capped inorganicnanoparticle deposited on the organic stripe phase layer, and an organicmolecule nucleated on the surface of the inorganic nanoparticle in aone-dimensional pattern.

In still another example, the present invention provides a particle-rodnanostructure comprising a mercaptoundecanoic acid-capped cadmiumselenide nanoparticle. The nanostructure further comprises one or morearachidic acid single-crystalline rods nucleated on themercaptoundecanoic acid-capped cadmium selenide nanoparticle in aone-dimensional growth pattern.

Further objects, features, and advantages of the present invention willbecome apparent from consideration of the following description and theappended claims when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a conceptual image of a particle-rodnanostructure formed on a stripe phase layer on a substrate inaccordance with one example of the present invention;

FIG. 2 is an elevated view of a conceptual image of the particle-rodnanostructure of FIG. 1;

FIG. 3 is an atomic force microscopy (AFM) image of spin-coatedparticle-rod nanostructures in accordance with one example of thepresent invention;

FIG. 4 is another AFM image of spin-coated particle-rod nanostructures;

FIG. 5 is a transmission electron microscope (TEM) image of cadmiumselenide nanoparticles prior to capping with mercaptoundecanoic acid inaccordance with one example of the present invention;

FIG. 6 is a TEM image of mercaptoundecanoic acid-capped cadmium selenidenanoparticles in accordance with one example of the present invention;

FIG. 7 is a table depicting elemental compositions of cadmiumselenide-mercaptoundecanoic acid capped nanoparticles; and

FIGS. 8 and 9 are AFM images of consecutive scans of the same area of aspin-coated particle-rod nanostructure in accordance with one example ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

An example of the present invention comprises a method of forming aparticle-rod nanostructure for electronic, optical, and bio-sensingapplications. The particle-rod nanostructure includes an inorganicnanoparticle and an organic crystalline rod formed from the surfacethereof in a one-dimensional growth pattern. One example of the methodof forming the nanostructure comprises preparing a mixture comprisinginorganic nanoparticles with a capping agent and an organic molecule ina solvent. The mixture is spin-coated to yield the particle-rodnanostructure on a substrate. In this example, the spin-coating causesevaporation of the solvent and involves precipitating an organic stripephase layer. Spin-coating further involves depositing the cappednanoparticle on the stripe phase layer and nucleating the organiccrystalline rod in a one-dimensional growth pattern from the surface ofthe nanoparticle.

When the solvent evaporates, the solvent “pools” or gathers about thenanoparticle, and nucleation of organic crystalline rods begins in aone-dimensional pattern. Nucleation may be defined as a stage in theprocess of forming the particle-rod nanostructure whereby organicmolecules, e.g., alkane derivatives, experience a phase transitionbetween an amorphous state and a crystalline state. Although not wantingto be limited by theory, it is believed that the clusters of the organicmolecules overcome a critical nucleation barrier wherein a criticalnucleation energy and a critical nucleation size are to be reached forthe organic molecular clusters to undergo a crystallization phasetransformation.

The inorganic nanoparticles serve as a “defect” within the organicmolecules and thus serve as a center for nucleation. That is, the defectfeature of the nanoparticles affects the critical nucleation barrier bylowering the critical nucleation energy, allowing the organic molecularclusters to more easily reach the critical size and nucleate from thesurface of the nanoparticle in a one-dimensional growth pattern. Oncethe critical size is reached, it is believed that there is athermodynamic driving force or kinetic affinity toward crystal growth inan anisotropic and one-dimensional manner, resulting in the organicnanorods. It is further believed that during spin-coating each of thenanoparticles traps solvent around it, causing high concentrations tooccur and activating nucleation of the organic nanorods in theone-dimensional pattern.

The nanoparticle of the present invention preferably comprises inorganicmaterials such as cadmium selenide nanocrystals. In one example, thecadmium selenide (CdSe) nanocrystals are of various sizes having adiameter between about 2 nanometers (nm) and 30 nm. Moreover, thenanocrystals may have varying aspect ratios (isometric nanoparticles andanisotropic nanoparticles (e.g., rods)). Cadmium selenide nanoparticlesexist in amorphous and crystalline states. In this example, the cadmiumselenide nanocrystals are preferably in the crystalline state. Althoughthe nanoparticles are preferably cadmium selenide nanocrystals, thenanoparticles may comprise other suitable nanoparticles such as themetal chalcogenide nanoparticles cadmium sulfide, cadmium telluride,zinc sulfide, zinc selenide, and lead sulfide. Additionally, goldnanoparticles may also be used.

The organic molecule, e.g., alkane derivative, in accordance with oneexample of the present invention comprises fatty acids and otheramphiphiles. In this example, the organic molecules are alkanederivatives, being long-chain carboxylic acids, and preferably arearachidic acid and stearic acid. However, phospholipids such as1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine and10,12-pentacosadiynoic acid, and metal ion complexes of fatty acids(also called fatty acid soaps) such as copper arachidate and manganesearachidate may be used without falling beyond the scope or spirit of thepresent invention.

The solvent of the present invention preferably comprises organicsolvents, including short-chain alcohols. For example, the solvent mayinclude methanol, ethanol, isopropanol (also called isopropyl alcohol),butanol, chloroform, tetrahydrofuran (THF), m-cresol, and mixturesthereof. In this example, ethanol or isopropyl alcohol is preferablyused.

The substrate in accordance with one example of the present inventionpreferably comprises highly oriented pyrolytic graphite (HOPG). Thecapping agent is preferably mercaptoundecanoic acid (MUA) ormercaptohexadecanoic acid (MHA).

Referring to FIGS. 1 and 2, organic crystalline rods 12 are formed bycrystalline lattice unit cells (here, arachidic acid unit cells)attaching to each other along the b direction during crystallization.FIGS. 1 and 2 show the crystalline packing structure of the organiccrystalline rod 12 in relation to a nanoparticle 13 along with a stripephase layer 14 and an HOPG layer 16. In this example, the alkyl chainincludes a zigzag plane that is substantially parallel to theparticle-rod interface, but substantially perpendicular to the HOPGsubstrate, unlike the underlying stripe phase layer wherein the alkylchain zigzag plane is parallel to the HOPG basal plane. This shows thatthe organic crystalline rods are nucleated directly from thenanoparticle.

In one method of the present invention, inorganic nanoparticles areprepared. In one example of the method, high-temperature cadmiumselenide (CdSe) nanoparticles are prepared. In this example, betweenabout 1 and 2 weight of cadmium oxide (CdO), between about 2 and 3weight % of tetradecylphosphonic acid (TDPA), and between about 95 and97 weight % of trioctylphosphineoxide (TOPO) are mixed together,defining a TOPO-TDPA mixture. The TOPO-TDPA mixture is slowly heated tobetween about 300 degrees Celsius (° C.) and 320° C. under an Argon (Ar)flow. At about 300° C., the cadmium oxide powder, having a reddish brownpigment, dissolves in the TOPO-TDPA mixture to form a homogeneouscolorless solution.

In this example, the temperature of the solution is then cooled down toabout 270° C., and a selenium (Se) solution of between about 0.5 and 1%weight is quickly injected therein. As a result, cadmium selenide (CdSe)nanocrystals are formed at about 250° C. over about 4 hours andprecipitated with methanol. At this stage, the CdSe nanocrystals have acombination of TOPO and TDPA capped on the surface thereof.

The cadmium selenide nanocrystals are then preferably thiolcoated/capped with a capping agent, e.g., mercaptoundecanoic acid (MUA).This may be accomplished by using molecular ratios of CdSe to MUAranging between about 1:3 and 1:10, and preferably 1:5. In this example,a molecular ratio between CdSe and MUA of about 1:5 is used. Themercaptoundecanoic acid is then dissolved in methanol. The pH balance ofthe MUA-methanol solution is adjusted to be greater than 10 preferablyusing tetramethylammonium hydroxide pentahydrate (TMAH).

In the absence of light, the precipitated CdSe nanocrystals aredissolved in the MUA-methanol solution. The resulting solution isstirred under an Argon flow for about 2 hours to form mercaptoundecanoicacid (MUA)-capped CdSe nanocrystals. Ethyl acetate and ethyl ether areused to precipitate and wash (repeatedly between about 2 and 3 times)the MUA-capped CdSe nanocrystals. Subsequently, the MUA-capped CdSenanocrystals preferably are dispersed in isopropanol to define a cadmiumselenide (CdSe) solution.

In this example, the solution of the organic molecule, e.g., anarachidic acid solution, and the CdSe solution (containing the MUA-CdSenanoparticles in isopropanol) are mixed to yield a molar ratio of about1:1 of the arachidic acid and the MUA-CdSe, defining a mixed solution tonucleate a growth of the organic molecule on the inorganic nanoparticledeposited on a substrate, yielding the particle-rod nanostructure. Inthis example of the present invention, the method further includesspin-coating the mixed solution. To accomplish this, the mixed solutionis dispensed onto freshly cleaved highly oriented pyrolytic graphite(HOPG) and spun at between about 1000 and 5000 rpm, preferably at about3,000 rpm, for about 60 seconds. A layer is then formed on the HOPGsubstrate. The relatively low solubility of the arachidic acid allowsfor the arachidic acid to then precipitate out and form an arachidicacid stripe phase layer on the HOPG substrate layer.

Although not wanting to be limited by theory, it is believed that as thesolvent evaporates during spinning the nanoparticles superficially trapremaining solvent thereabout. During spinning, the nanoparticles arethen deposited on the stripe phase layer. It is believed that theformation of the stripe phase layer allows the nanoparticles to depositthereon due to an affinity between the capping agent (MUA) and theorganic molecule (arachidic acid). The nanoparticles serve as a defectwithin the stripe phase layer, lowering the critical energy ofcrystallization of the organic molecule. Thus, when its critical size isreached, the organic molecule crystallizes on the surface of thenanoparticle. The trapped solvent about the nanoparticles and thenucleation driving force and kinetics allow crystallization growth in aone-dimensional pattern defining the particle-rod nanostructure.

FIGS. 3 and 4 are AFM images of the arachidic acid film spin-coated fromisopropanol depicting the stripe phase layer of this example. In thisexample, the stripe phase layer has a film thickness of 0.4 nm and abilayer periodicity of 5.6 nm. Spin coating of the MUA-CdSe isopropanolsolution was found to yield relatively few particles trapped on the HOPGlayer. However, when a stripe phase layer is spin-coated from a mixedisopropanol solution of arachidic acid and MUA-CdSe, the particle-rodhybrid structure spontaneously forms (see FIGS. 3 and 4). In thisexample, it was found that the particle heights may range from betweenabout 3.5 and 30 nm.

FIGS. 5 and 6 depict TEM of uncapped and capped CdSe nanoparticles,respectively. This suggests that the relatively smaller particles(between about 3.5 and 15 nm) are discrete particles, whereas therelatively larger particles (between about 15 and 30 nm) are aggregatesformed upon MUA photooxidation. In the results of this example, theorganic crystalline rods have relatively identical height (0.95±0.09 nm)and width (5.39±0.05 nm) but a length distribution (between about 50 nmand 250 nm). The number of rods per particle varies with the molar ratioof MUA to CdSe.

In one example, when the molar ratio of MUA:CdSe=0.38:1, the averagenumber of rods per particle is about 1.9. An average of 2.8 rods emanatefrom each particle, when MUA:CdSe=0.50:1. As shown, the organiccrystalline rods radiating from the inorganic nanoparticles displayrandom orientations unlike the stripe phase layer, which exhibits thethree-fold symmetry of the HOPG substrate layer. An analysis of multipleimages indicates that relatively high percentages (approximately 40%) ofrods are substantially parallel to each other with a center-to-centerseparation of about 18 nm.

FIG. 8 shows that the particle-rod nanostructure forms on the stripephase layer that precipitated on the substrate. FIG. 9 shows that someorganic molecules are transferred from the organic rods to the stripephase layer (indicated by the arrow) by the scanning tip in a subsequentscan of the same area. The transferred organic molecules provide supportthat the rods are made of the same organic molecules (here arachidicacid molecules). The length of the stripe phase layer in FIG. 9 is about280 nm (two new stripes plus the extension of the existing stripes) andabout 140 nm of the molecular rod is lost. This shows that the rodsinclude about twice the number of organic molecules as the stripe phaselayer of the same length.

Upon solvent evaporation during spin coating in this example, theorganic molecule precipitates first to self-assemble into the orderedstripe phase layer due to its low solubility and one-dimensionalepitaxial interaction with the HOPG lattice. In this example, it isbelieved that the arachidic acid monolayer immobilizes the MUA-CdSenanoparticles, which likely trap a small amount of liquid by defectpinning of the three-phase line during the last stage of solventevaporation. Upon continued evaporation, the nanoparticles deposit onthe stripe phase layer and heterogeneous nucleation of an organic rod isinduced by the nanoparticles, resulting in the one-dimensional growth ofthe organic molecular crystals (here arachidic acid crystals). The rodformation may be due to the presence of a highly curved surface of thenanoparticle or as a result of strong undercooling conditions of thespin coating, which also favors unidirectional growth with the growthdirection substantially perpendicular to the growing interface.

Although not wanting to be limited to theory, it is believed that theintermolecular forces between alkyl chains favor parallel attachment ofthe zigzag chain plane of the organic molecule to the interface. Theresults show that the nanoparticles serve as nano-seeds in nucleatingnano-size crystalline rods composed of organic molecules, in which thecross-sectional area is defined by one unit cell. The intermolecularforces between MUA and the solvent are a likely factor for the liquidpinning because without MUA, the CdSe nanoparticles may not bedispersible and therefore may not be wettable by the solvent. In thisexample, the mutual interactions between MUA and arachidic acid (eitherhydrogen bonding at their terminal carboxylate groups or non-polarinteractions between the respective alkyl chains) allow the CdSeparticles to be immobilized on the substrate, and may also beresponsible for the heterogeneous nucleation of the arachidic acid rods.

EXAMPLE

This example provides a method of forming a particle-rod nanostructurefor use in various applications, e.g., electronic, optical, andbio-sensing applications. In this example, the following chemicalsolutions and components were purchased or prepared:trioctyiphosphineoxide (TOPO, 90%), CdO (99.99%), Se powder (99.5%),trioctylphosphine (TOP, 90%), 11-mercaptoundecanoic acid (MUA, 95%),tetramethylammonium hydroxide pentahydrate (TMAH, 97%) (purchased fromSigma-Aldrich Corp.), ethyl acetate and ethyl ether (purchased fromFisher Scientific) and n-tetradecylphosphonic acid (TDPA, 98%)(purchased from Alfa Aesar Co.).

The high-temperature CdSe nanoparticle synthesis was performed. In thesynthesis of CdSe nanocrystals, 0.0514 gram (g) of CdO, 0.1116 g ofTDPA, and 3.7768 g of TOPO were slowly heated to between about 300° C.and 320° C. under Ar flow. At about 300° C., the reddish brown CdOpowder dissolved in the TOPO-TDPA mixture to form a homogeneouscolorless solution. The temperature of the solution was then cooled toabout 270° C., and a selenium stock solution (0.0314 g of Se powder in2.4 mL of TOP) was quickly injected in to the TOPO-TDPA mixture. Theresultant CdSe nanocrystals were grown at about 250° C. for about 4hours and precipitated with methanol. This completed thehigh-temperature cadmium selenide nanoparticle synthesis.

Thiol coating of CdSe nanocrystals was then performed using varyingmolecular ratios of CdSe:MUA at 1:3, 1:5, and 1:10. An amount (e.g.,0.4672 g of MUA, if CdSe:MUA ratio is 1:5) of MUA was dissolved in 15 mLof methanol. The pH of the resulting solution was adjusted to greaterthan about 10 by using tetramethylammonium hydroxide pentahydrate. Inthe absence of light, the methanol-precipitated CdSe nanocrystals weredissolved in the above mixture and the resulting solution was stirredunder Ar flow for 2 hours. Ethyl acetate and ethyl ether were used toprecipitate and wash thrice the MUA-capped nanocrystals, which were thendispersed in isopropanol to form the CdSe solution.

A TEM analysis (see FIGS. 5 and 6) was conducted in bright-field modeusing a JEOL FastEM 2010 HR TEM electron microscope with a LaB₆thermoelectric emission gun working at 200 kV. As-prepared nanocrystalswere dissolved in methanol, and placed on a 200-mesh copper carbon grid.The solvent was dried by evaporation. A number of SEM images wereobtained using a Hitachi S-2400 microscope at 25 keV in secondaryelectron mode. Vacuum dried (under dark conditions) CdSe-MUAnanocrystals were spread on carbon adhesive tabs on an aluminum stub. Anin-situ EDAX unit (EDAX Inc. PV 9900) attached to the SEM was used todetermine the elemental composition of the CdSe-MUA nanoparticles (seethe table of FIG. 7).

Stock solutions of arachidic acid (>99%, Sigma-Aldrich) and MUA-CdSenanoparticles in isopropanol (Fisher Scientific, spectranalyzed) weremixed to yield about 0.1 mM arachidic acid and about 0.1 mM MUA-CdSenanoparticles. About 100 μL of the mixed solution was dispensed onto afreshly cleaved HOPG surface spinning at 3000 rpm for 60 seconds. Thespin-coated samples were imaged (FIGS. 3, 4, 8, 9) using a Dimension3100 AFM (Veeco Metrology). Height, amplitude, and phase images wereobtained in Tapping Mode in ambient air with silicon tips (TESP, Veeco)using a scan rate of 1 Hz. Integral and proportional gains were found tobe approximately 0.3 and 0.5, respectively. The films were imaged (FIGS.3, 4, 8, 9) after film preparation. The crystal structure of stearicacid was constructed with the Materials Studio software program(Accelrys, Inc.).

Further description of the present invention may be found in“Particle-Rod Hybrids Growth of Arachidic Acid Molecular Rods FromCapped Cadmium Selenide Nanoparticle,” Journal of the American ChemicalSociety, Vol. 126, pp 16290-16291 (25 Nov. 2004), Dongzhong Chen et al.,the entire contents of which are incorporated herein by reference.

While various embodiments for carrying out the invention have beendescribed in detail, those familiar with the art to which this inventionrelates will recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

1. A method of forming a particle-rod nanostructure, the methodcomprising: preparing a mixture comprising an inorganic nanoparticle andan organic molecule in a solvent; and spin-coating the mixture tonucleate the crystal growth of the organic molecule on the inorganicnanoparticle that is deposited on a substrate, yielding the particle-rodnanostructure.
 2. The method of claim 1 wherein the inorganicnanoparticle includes one of cadmium selenide nanocrystals; metalchalcogenide nanoparticles; gold nanoparticles, and mixtures thereof. 3.The method of claim 2 wherein the metal chalcogenide nanoparticlesinclude one of cadmium sulfide, cadmium telluride, zinc sulfide, zincselenide, lead sulfide, and mixtures thereof.
 4. The method of claim 1wherein the organic molecule includes one of carboxylic acids,phospholipids, metal ion complexes with fatty acids, and mixturesthereof.
 5. The method of claim 4 wherein the alkane carboxylic acidsinclude one of arachidic acid, stearic acid, and mixtures thereof; thephospholipids include one of1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine, 10,12-pentacosadiynoicacid, and mixtures thereof; and the metal ion complexes with fatty acidsinclude one of copper (II) arachidate, manganese (II) arachidate, andmixtures thereof.
 6. The method of claim 1 wherein the solvent includesone of methanol, ethanol, isopropanol, butanol, chloroform,tetrahydrofuran (THF), m-cresol, and mixtures thereof.
 7. The method ofclaim 1 wherein the inorganic nanoparticles are capped with a cappingagent.
 8. The method of claim 7 wherein the capping agent includesalkanes modified with thiols at one end and carboxylic acid groups atanother end.
 9. The method of claim 8 wherein the carboxylic acid groupsinclude one of mercaptoundecanoic acid (MUA), mercaptohexadecanoic acid(MHA), and mixtures thereof.
 10. The method of claim 1 wherein thesubstrate is highly oriented pyrolytic graphite, substrates wettable bythe solvent including oxidized silicon wafer coated by a layer oforganosilanes, the organosilanes including one ofoctadecyltrichlorosilane, aminobutyldimethylmethoxysilane, and mixturesthereof.
 11. The method of claim 1 wherein the step of preparing themixture comprises: preparing inorganic nanocrystals; coating theinorganic nanocrystals with a capping agent to define the inorganicnanoparticles; and mixing the inorganic nanoparticles with the organicmolecule in solvent to define the mixture.
 12. The method of claim 11wherein the mole ratio of the inorganic nanoparticles to the cappingagent obtained ranges between about 1:0.1 and 1:1.
 13. The method ofclaim 1 wherein spin-coating comprises: spinning the mixture betweenabout 1000 and 5000 rotations per minute; evaporating the solvent duringspinning; precipitating an organic stripe phase layer on the substrate,the organic stripe phase layer defined by a plurality of organicmolecules arranged in ordered strips; depositing the inorganicnanoparticles on the organic stripe phase layer; and nucleating aone-dimensional assembly of organic molecules on the surface of theinorganic nanoparticle to define the particle-rod nanostructure.